Components, for example turbine blades, turbine vanes, combustion chamber walls, of gas turbine engines and other turbomachines are cooled to maintain the component at a temperature where the material properties of the component are not adversely affected and the working life and the integrity of the component is maintained.
One method of cooling components, turbine blades, turbine vanes combustion chamber walls, of gas turbine engines provides a film of coolant on an outer surface of a wall of the component. The film of coolant is provided on the outer surface of the wall of the component by a plurality of effusion cooling apertures which are either arranged perpendicular to the outer surface of the wall or at an angle to the outer surface of the wall. The effusion apertures are generally manufactured by laser drilling, but other processes may be used, e.g. electro-chemical machining, electro-discharge machining or by casting. Effusion cooling apertures are often cylindrical and angled in the direction of flow of hot fluid over the outer surface of the component. Angled effusion cooling apertures have an increased internal surface area, compared to effusion cooling apertures arranged perpendicular to the outer surface of the wall of the component, and the increased internal surface area increases the heat transfer from the wall of the component to the coolant. Angled effusion apertures provide a film of coolant on the outer surface of the component which has improved quality compared to effusion cooling apertures arranged perpendicular to the outer surface of the wall of the component.
However, despite the use of cylindrical effusion cooling apertures angled in the direction of flow of hot fluid over the surface of the component, the coolant passing through the cylindrical effusion cooling apertures often retains a significant component of velocity in direction perpendicular to the surface of the component. This causes the jets of coolant exiting the cylindrical effusion cooling apertures to detach from the surface of the component and results in a poor film of coolant on the surface of the component. The high velocity of the jets of coolant also increases the mixing between the coolant and the hot fluid flowing over, or a hot fluid adjacent to, the surface of the component and this raises the temperature of the film of coolant and therefore reduces its cooling effect. Additionally there may be relatively large distances between adjacent effusion cooling apertures and this may result in a film of coolant which is non-uniform across the surface of the component and hence there may be hot spots on the surface of the component between effusion cooling apertures.
The use of a larger number of smaller diameter effusion cooling apertures, compared to a smaller number of larger diameter effusion cooling apertures, may be used to increase the internal surface area of the angled effusion apertures for the same total mass flow of coolant. However, it is expensive and time consuming to drill a large number of effusion cooling apertures using conventional manufacturing techniques, e.g. laser drilling, electro-chemical machining or electro-discharge machining.
The use of fanned effusion cooling apertures provides enhanced film cooling effectiveness, but fanned effusion cooling apertures have un-aerodynamic diffusion which suffers from flow separation and reduces its cooling effect.
Therefore the present invention seeks to provide a novel cooled component which reduces or overcomes the above mentioned problem.